VHF/UHF self-tuning planar antenna system

ABSTRACT

A wide-band self-tuning antenna system for the reception of VHF/UHF signals includes planar antenna elements located on both the surfaces of a printed circuit board and a tuner unit which includes a plurality of matching networks for the respective plurality of bands of frequencies. The planar elements on the respective surfaces of the printed circuit board are substantially identical in shape.

This application claims priority from provisional applications Nos.60/067,620, filed Dec. 5, 1997 and No. 60/100,743, filed Sep. 17, 1998.

FIELD OF THE INVENTION

The present invention concerns antenna systems for receiving broadcastsignals such as television signals.

BACKGROUND INFORMATION

Conventional indoor TV antenna systems generally include two separateantennas for respective VHF and UHF reception. The antenna for receivingthe VHF bands employs a pair of telescopic elements forming a dipolewith each of the elements having a maximum length of from 4 to 6 feet(1.5 to 2.5 m). The two elements usually are mounted to permit theelements to be spread apart to increase or shorten the dipole length andthose elements are commonly referred to as “rabbit ears.” The indoor UHFantenna typically is a loop having a diameter of about 7½ inches (20cm).

One problem associated with the conventional indoor antenna systems isthat the physical dimension of the VHF dipole is undesirably long forthe ordinary setting in a living room and that the length as well as thedirection of the dipole elements may need to be adjusted depending uponthe receiving channels. The second problem is that the performance ofsuch conventional indoor VHF/UHF antennas changes in response to changesof the physical conditions around the antenna elements. For example, itis difficult for a user to make proper adjustment of the antennas sincea human body coming into contact with an antenna changes theelectro-magnetic conditions associated with the antenna elements. Thethird problem is that the conventional indoor antenna systems do notalways provide a sufficient signal level for good reception.

A need exists for an antenna system including compact-size antennaswhich are capable of receiving a sufficient level of signals throughoutthe entire VHF/UHF broadcast bands of frequencies without any physicaladjustments. Further, there is need for such an antenna system that canbe used in either indoor or outdoor applications.

SUMMARY

In accordance with the present invention, an antenna system forreceiving VHF/UHF broadcast signals comprises a planar antenna and atuner unit which includes a tuning arrangement. A gain controllableamplifier may be included in the tuner unit where necessary. The planarantenna includes a pair of antenna elements which are substantiallyidentical in shape. These elements are located on the respectivesurfaces of a dielectric board. The tuning arrangement includes aplurality of matching networks for the respective plurality of bands ofbroadcast frequencies.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 illustrates an embodiment of the aspects of the disclosed planarantenna system which includes a planar antenna and a tuner unitincluding a tuning arrangement and a gain controllable amplifier;

FIG. 2 illustrates an exemplary application for the use of the planarantenna system;

FIG. 3 illustrates another exemplary application for the use of theplanar antenna system;

FIG. 4 illustrates a top view of an embodiment of the planar antenna;

FIG. 5 illustrates a bottom view of the embodiment of the planar antennashown in FIG. 4;

FIG. 6 illustrates VSWR characteristics (50-800 MHz) of the embodimentof the planar antenna.

FIG. 7 illustrates a radiation pattern of the embodiment of the planarantenna at one of the low-band VHF television channel frequencies (67.25MHz); and

FIGS. 8-10 are schematic diagrams of an embodiment of the aspects of thedescribed tuner unit which includes a plurality of selectable matchingnetworks and a gain controllable amplifier controlled by a built-in AGCarrangement.

In the various figures, the same or similar elements shown areidentified by the same reference numbers.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In this application, the term “television apparatus” is used to describeany television apparatus which includes at least one television tuner(such as television receivers, VCR's, etc.).

FIG. 1 illustrates a VHF/UHF planar antenna system embodying the aspectsof the present invention. The planar antenna system includes planarantenna 10 and tuning unit 30. Planar antenna 10 and tuning unit 30 arecoupled by a coaxial cable 20. As to this exemplary embodiment, thecharacteristic impedance of coaxial cable 20 is 75Ω.

Tuner unit 30 includes tuning arrangement 31 and gain controllableamplifier 33. Gain controllable amplifier 33 is optional and may not beincluded in tuner unit 30 where the television broadcast signals aresufficiently strong. Tuning arrangement 31 includes a plurality ofimpedance matching networks 610 (e.g., bandpass filters) for therespective plurality of bands of broadcast frequencies (see FIG. 8 fordetail). Common infrared (IR) remote controller 40 is used to selectboth the matching networks in tuning unit 30 and the channels fortelevision apparatus 50 simultaneously. Of course, a separate IR remotecontroller can be utilized to select a proper matching networkindividually. The gain of amplifier 33 is controlled automatically by abuilt-in automatic gain control (AGC) arrangement (see FIGS. 8-10 forthe schematics).

FIG. 2 illustrates one of the applications for indoor use of the planarantenna system. Here planar antenna 10 is located inside of planarantenna case 11 which is made of dielectric materials. Antenna case 11,including planar antenna 10, hangs on the wall while tuner unit 30 isplaced on the top of television apparatus 50. Coaxial cable 20 is usedto couple between planar antenna 10 and tuner unit 30. Antenna case 11can be designed to be waterproof for outdoor uses.

FIG. 3 illustrates another application for the use of the planar antennasystem. Here tuner unit 30 is located underneath antenna case 11 whichis placed on the top of television apparatus 50.

FIGS. 4 and 5 illustrate respective top and bottom views 100, 200 ofplanar antenna 10. The antenna elements of planar antenna 10 aredifferent from those of the traditional dipole (rabbit ears) or loopantennas in many aspects. In particular, the elements are developedbased upon microstrip techniques, and the unique patterns of theelements make it possible for the planar antenna system to provideomini-directional reception of the television signals as can be seenfrom the radiation pattern characteristic of the antenna that is shownin FIG. 7. Thus, no adjustment for the direction of the antenna isnecessary once installed. This omini-directional feature in thehorizontal platform is believed to result from the fact that themajority of RF current flows along the edges of every one of the planarantenna elements.

As to the exemplary embodiment shown in FIGS. 4 and 5, the antennaelements are etched directly on a printed circuit board (PCB), such asthe model “MC3D” Medium Frequency Laminate, manufactured by GlasteelIndustrial Laminates (0.062″ thickness, double-side PCB board withdielectric constant of 3.53+/−0.08). The dimension of the PCB isapproximately 12 by 12 inches (30×30 cm). Both VHF and UHF antennaelements are formed on each side of the PCB, and VHF and UHF elements onone side are substantially identical, in shape, to respective VHF andUHF elements on the other side of the PCB. In addition, the former arerotated 90 degrees with respect to the latter.

The VHF antenna elements feature a unique “H”-shape configuration. Theantenna element on each end of the “H” shape is approximately 2.5 inches(6.5 cm) width×12 inches (30 cm) long. Both ends of the “H” shape areconnected together with approximately 1 inch (2.5 cm) width by 7 inches(17.5 cm) long of microstrip transmission line to complete the “H”shape. As described above, the two “H”-shape VHF elements on therespective sides of the PCB are substantially identical in shape, andthe VHF element on the top side rotates 90 degrees from that on thebottom side of the PCB.

Each one of the “H”-shape elements for VHF signals is formed as acombination of the following three separate regions (Reference numbersfor the respective corresponding regions on the bottom side are shown inthe parenthesis): {circle around (1)} “S”-shape main region 120 (220);{circle around (2)} first supplemental region 150 (250); and {circlearound (3)} a second supplemental region 160 (260). First supplementalregion 150 (250) is approximately 2.5 inches (6.5 cm) width by 5.4inches (13.7 cm) length and separated from main region 120 (220) by agap of approximately one-tenth inch (2.5 mm). First supplemental region150 (250) is electrically coupled to main region 120 (220) throughinductor 151 (251), for example, 100 μH high Q surface-mounted chipinductor. It has been found that this arrangement extends the effectiveelectrical length of main region 120 (220).

Second supplemental region 160 (260) is substantially identical to firstsupplemental region 150 (250) in dimensions. Second supplemental region160 (260) is coupled to main region 120 (220) through capacitor 161(261), for example, 15 pF surface-mounted chip capacitor. It has beenfound that second supplemental region 160 (260) coupled via capacitors161 (251) significantly improves the overall voltage standing wave ratio(VSWR) characteristics of the planar antenna for the lower VHFtelevision band of frequencies (50-88 MHz).

There is a reflector region 140 only on the top side of the PCB.Reflector region 140 functions as a reflector for first supplementalregion 150. It has been found that reflector region 140 improves theoverall performance of the planar antenna in the upper VHF televisionband of frequencies (174-216 MHz).

UHF antenna elements 170, 270 feature an “H”-shape configuration as welland formed on the respective sides of the PCB. As described above, thesetwo UHF elements are also substantially identical in shape, and onerotates 90 degrees from the other.

Each end of the “H” shape element is square in shape and isapproximately 2.5 inches (6.5 cm) width by 2.5 inches (6.5 cm) length.The two ends are connected together with approximately 1 inch (2.5 cm)width by 1.5 inches (3.8 cm) length microstrip transmission line to formthe “H”-shape configuration. UHF element 170 (270) is coupled to theapproximately middle point of the microstrip transmission line of theVHF element 120 (220) through inductor 171 (271), e.g., 100 μH high Qsurface-mounted chip inductor.

The top side of the PCB also include a ground plane region 130. Groundplane region 130 is square in shape and is approximately 2.5 by 2.5inches (6.5×6.5 cm). Female “F” connector 131 is located on ground planeregion 130. The feet (ground line) of connector 131 is connected to bothground plane region 130 and, by piercing through the PCB, another groundplane region 230 on the bottom side of the PCB. The dimension of groundplane region 230 is approximately 2.5 inches (6.5 cm) width by 6.5inches (16.5 cm) length. The signal line of connector 131 is connectedto signal transmission line 132 formed on the top side of the PCB. Ithas been found that both of ground plane regions 130, 230 contribute tothe stabilization of the overall performance of the planar antennasystem notwithstanding the changes of the physical conditions around theplanar antenna.

As shown in FIG. 4, a 4:1 balun transformer 133 is located on the topside of the PCB for impedance matching between the planar antennaelements and coaxial cable 20. Ends of the first winding of transformer133 are coupled to respective ones of connecting point 136 andconnecting region 134. Connecting point 136 is located approximately atthe middle of the transmission line of VHF elements 120. Connectingregion 134 is connected to connecting point 234 of VHF element 220 onthe bottom side via two through-holes. Ends of the second winding arecoupled to respective transmission line 132 and ground plane 130.Matching capacitor 135 (4 pF) is coupled between the center of thesecond winding and ground plane 130 for better impedance matching.Alternatively, a variable capacitor (2-6 pF) may be coupled between thetwo ends of the second winding as shown in FIG. 8.

Another characteristics of the planar antenna is that unlikeconventional microstrip antennas, there is no flat ground plane regionon the bottom side of the PCB, which entirely covers the region beneaththe antenna elements formed on top side of the PCB. As to conventionalmicrostrip antennas, the bandwidth of such antennas is proportional tothe distance between the antenna elements on one surface and flat groundplane region on the other side of the substrate used (i.e., thethickness of the substrate). It has been found that the elimination ofthis type of flat ground plane region contributes to the wide-bandcharacteristic of the planar antenna. As a reference, see Munson, RobertE., “Microstrip Antennas” in Antenna Enaineerina Handbook (3rd ed.)(McGraw Hill, 1993).

FIG. 8 shows the schematic diagram of a portion of tuner unit 30 whichincludes a plurality of matching networks. As to this particularexemplary embodiment, five bandpass filters 610 (BPF's) are utilized asmatching networks, and they are pre-tuned to respective ones of fivedifferent bands of broadcast frequencies. They are the following:

VHF 1: 54-72 MHz (Channels 2 to 4 in the U.S.)

VHF 2: 76-88 MHz (Channels 5 to 6 in the U.S.)

VHF 3: 174-192 MHz (Channels 7 to 9 in the U.S.)

VHF 4: 192-216 MHz (Channels 10 to 13 in the U.S.)

UHF: 470-800 MHz (UHF Channels in the U.S.)

As shown in FIGS. 8-10, the band selection is to be made in accordancewith receiving channels. A user selects a proper band by using an IRremote controller. However, this selection can be done automatically inresponse to the level of the automatic gain control (AGC) signal forgain controllable amplifier 33 a. The AGC signal works to reduce thegain of amplifier 33 a when a proper matching network is selected for areceiving channel.

By virtue of the AGC arrangement, the level of the output signal oftuning unit 30 is maintained at a desirable pre-determined level,regardless of the variation of the strength of the received televisionsignals throughout an entire band of frequencies.

In the exemplary embodiment shown in FIGS. 8 and 9, the AGC arrangementincludes gain controllable amplifier 33 a; signal amplifier stage 720;signal splitter 710; DC rectifier 730; and DC offset voltagecompensation circuitry 750. It has been found that a combination of aplurality of selectable front-end band pass filters 610 and thesubsequent AGC arrangement makes AGC operate properly throughout theentire VHF/UHF television bands of frequencies (50-800 MHz).

For faster adjustment of amplifier 33 a, a microprocessor ay be utilizedto control the gain of amplifier 33 a together with a memory whichstores information on the desirable AGC levels for respective broadcastchannels.

In addition, tuning unit 30 may further include an RF signal selectionswitch which allows a user to select between RF signals from the planarantenna and those from other signal sources (e.g., a satellite dish,cable, VCR, etc.).

In FIG. 10, Infrared remote sensor arrangement 800 includes IR signalreceiver 830, microprocessor 810, multiplexer 850, five light emittingdiodes (LED's) and two manually controlled switches R, L.

LED1, LED2, LED3, LED4 and LED5 indicate the selections of respectiveones of five different bands of broadcast frequencies, namely VHF-1,VHF-2, VHF-3, VHF-4 and UHF in FIG. 8. That is, the five LED's indicatethe selections of respective ones of five different BPF's 610. Forexample, LED 1 turns on when the BPF for VHF-1 is selected. Manualswitches R, L function as “tup-down” switches for the band selection sothat a user without a remote controller may still select proper bands offrequencies.

IR receiver 830 coupled to microprocessor 810 receives IR signals fromthe remote controller. Then microprocessor 810 generates controlsignals.

In response to the control signals, multiplexer 850 coupled tomicroprocessor 810 sends band selection signals A. B. C. D. E torespective ones of PIN diodes D1, D2, D3, D4 and D5. Here, multiplexer850 functions as a plurality of digitally-controlled analog switches.Power supply arrangement 840 includes two voltage regulators 870, 890.

While the invention has been described with reference to a preferredembodiment, it is understood that the words which have been used hereinare words of description, rather than words of limitation. Numerousalterations of, or modification to, the antenna system of the presentinvention may occur to one skilled in the art without departure from thespirit and scope of the invention and the principles and featuresthereof. For example, the planar antenna system can be used not only forreceiving digital and/or analog television signals but also forreceiving digital and/or analog audio or data signals.

What is claimed is:
 1. A planar antenna for receiving VHF/UHF signalscomprising: a dielectric substrate having first and second surfaces onwhich first and second conductive patterns are located respectively;each of said first and second conductive patterns including elementsforming respective first and second H-shaped patterns; said first andsecond H-shaped patterns forming first and second antenna elementsrespectively; said first and second antenna elements being substantiallyidentical in shape; and said first antenna element being rotatedsubstantially 90 degrees with respect to the second antenna element. 2.The planar antenna of claim 1, wherein: each of said first and secondconductive patterns form a respective plurality of antenna elements. 3.The planar antenna of claim 1, wherein: each of said first and secondconductive patterns further form respective ground plane regions.
 4. Theplanar antenna of claim 1, wherein: the antenna elements being formed onthe first and second surfaces in respective first and second patternsfor providing a substantially omnidirectional reception of a televisionsignal.
 5. The planar antenna of claim 1, further comprising: anamplifier for amplifying signals received by said antenna elements;control means for controlling the gain of said amplifier in response tothe level of said received signals; and a plurality of matching networksfor providing impedance matching between said antenna elements and saidamplifier within the respective plurality of bands of frequencies. 6.The planar antenna of claim 2, further comprising: an amplifier foramplifying signals received by said antenna elements; control means forcontrolling the gain of said amplifier in response to the level of saidreceived signals; and a plurality of matching networks for providingimpedance matching between said antenna elements and said amplifierwithin the respective plurality of bands of frequencies.
 7. The planarantenna of claim 3, further comprising: an amplifier for amplifyingsignals received by said antenna elements; control means for controllingthe gain of said amplifier in response to the level of said receivedsignals; and a plurality of matching networks for providing impedancematching between said antenna elements and said amplifier within therespective plurality of bands of frequencies.
 8. The planar antenna ofclaim 4, further comprising: an amplifier for amplifying signalsreceived by said antenna elements; control means for controlling thegain of said amplifier in response to the level of said receivedsignals; and a plurality of matching networks for providing impedancematching between said antenna elements and said amplifier within therespective plurality of bands of frequencies.